The main objective of this project is to study the induction and maintenance of EBV-specific CD8+ T lymphocyte responses across the age spectrum. The major hypothesis to be addressed is that qualitative and quantitative changes in EBV and EBV epitope-specific CD8+ T lymphocyte responses will be observed over time. Age at acquisition of infection, recurrent exposure to EBV proteins, and changes in EBV protein expression over time will likely influence the EBV-specific CD8+ T lymphocyte responses in infants, children, adolescents, and adults from acute infection through convalescence/chronic infection. We will first use intracellular cytokine assays to identify the hierarchy of EBV lytic and latent protein-specific responses. Immunodominant epitopes within the most commonly recognized EBV proteins that are restricted by common HLA alleles will be defined. Tetramers representing immunodominant epitopes will be made and used to serially measure epitope-specific CD8+ T cells. Changes in EBV and EBV epitope-specific CD8+ T cell specificity and frequencies will be correlated with peripheral blood EBV load. In Specific Aim 2, we will characterize the phenotypes and f and functional properties of EBV epitope-specific CD8+ T lymphocytes. The cell surface phenotypes, cellular turnover, and activation state of EBV epitope-specific CD8+ T lymphocytes. The cell surface phenotypes, cellular turnover, and activation state of EBV epitope-specific CD8+ T cells will be evaluated using tetramer staining, along with monoclonal antibodies to cell surface antigens. We will then examine functional properties (lytic function, chemokine/cytokine secretion) and TCR usage of EBV epitope-specific T cells. Data form these studies will contribute to our understanding of age-related susceptibility to and clinical manifestations of EBV infection. Improved understanding of the evolution of EBV-specific CD8+ T lymphocytes should also prove helpful in the development of a prophylactic vaccine.